To achieve acceptable shelf-life, food and drink products require some degree of primarily physical but occasionally chemical processing. This creates a number of issues. Firstly, anything that delays the delivery of the foodstuff from source to destination is a cost.
Secondly, food and drink raw materials and products are highly susceptible to both microbial contamination and/or organoleptic deterioration. The longer the delay between product manufacture and arrival at the end-user, the greater the amount of spoilage and degree of deterioration. This, in turn, increases the amount of processing needed to minimize spoilage and/or loss. This, in turn, generates the need for more energy and more cost.
And finally, the longer the timescale between arriving at the end user and its ultimate consumption, the more the foodstuff requires additional energy consumption in the form of cooking and cooling or refrigeration or preservation.
Escalating processing costs, and particularly energy costs, in the form of cooking/cooling, refrigeration, or storage and distribution, are becoming a very major issue with many food and drink products. So much so that we often find that the container holding the food product costs more than the food product itself and the energy costs in producing and holding the food within the container in a safe and wholesome manner, cost more than the combined costs of the food and its container.
So, methods of preserving food without incurring large energy consumption during processing and/or consuming energy during storage, coupled with other cost reductions, are receiving increasing attention.
It is well-known that methods of extending shelf-life, such as smoking and cooking for foodstuffs and water cooling for liquids have been known for thousands of years, long before the role of spoilage and pathogenic micro-organisms was known or the role of chemical oxidation identified.
There are four primary types of food treatment for the purpose of extending shelf-life and minimizing pathogenicity, namely preservation, stabilization, pasteurization and sterilization. Each of these entails a different ratio of the amount of heating and cooling being applied with the more heating involved the less the amount of refrigeration required. Preservation, in the form of refrigeration, imparts no heating into the process and maintains many foods at their highest quality but with minimal shelf-life. However, if the degree of refrigeration is increased, e.g. freezing, the shelf-life increases but quality attributes tend to decrease.
While there are a wide range of factors involved in deciding which processing methods is most suitable for each application, including the amount of shelf-life required, the availability of refrigeration before and after processing, the robustness of the foodstuff raw materials or finished products, the prevalence of spoilage and/or pathogenic organisms, and the value of the raw materials and/or finished products, it is the absolute costs and the cost to value ratio that play a major role in the decision-making of the chosen preservation method.
Despite the extensive selection of methods available, (summarized in Newman, U.S. PA 61/480,521), one method, that involving the heating and cooling of the foodstuff using a thermal processing medium usually air, water or steam, is by far the most prevalent whether domestic or industrial in nature. Again, this approach is also found in many different variants such as the use of dry or wet heat, continuous or batch, static or moving, aseptic or non-aseptic environments, etc.
Continuous sterilization has been commercially available for almost 50 years and is the process of choice for manufacturers of large volume monoculture production, i.e. high throughput of the same products such as beans, soups and ketchup. While such systems involve major capital expenditure at the outset, over time it becomes increasingly cost effective. It allows very large volumes of product, often in excess of 400 units per minute to be continuously processed.
However, it was originally designed at a time when availability of refrigeration in the domestic environment was low and the demand for cost-effective production was high. It was also designed in an era where energy costs where comparatively low and freely available. So, in the modern processing environment, it has several limiting factors.
The initial capital costs are high, the running costs, especially energy costs, are also high. The considerable system infrastructure needed to withstand the high temperatures and pressures also absorbs a large percentage of the available energy. It is relative inflexible as it requires considerable equilibration time for a product changeover. It also has little buffering capacity so product has to completely exit from one chamber/tower before system changes can be enacted. In practice, the only parameter within the continuous sterilization environment that can be easily adjusted is speed of throughput/dwell time.
While there have been a continuous stream of incremental improvements to the established, continuous sterilization technologies (as typified by the teachings of Ono, U.S. Pat. No. 7,008,659 and Perren, U.S. patent application Ser. No. 12/648,067), Newman teaches novel methods, applications and apparatus for enhancing and optimizing process performance (U.S. PA 61/483,923), significantly improved system process control (U.S. PA 61/478,491), increased flexibility in the use of modern, lower cost packaging materials (U.S. PA 61/478,190) and enhanced finished product organoleptic properties, through improvements in enhanced product cooling (U.S. Pat. No. 478,665). He also teaches a novel method and apparatus for enhanced, controlled continuous sterilized food and drink manufacturing using apparatus that significantly reduces capital equipment costs while greatly improving manufacturing flexibility, (U.S. PA 61/480,521). Most recently (U.S. PA 61/488,220), he teaches a method which incorporates all of the above mentioned enhancements into the original vertical process but removes significant amounts of processing cost from the continuous pasteurization and sterilization by largely eliminating the need for system pressurization, (All of these applications are hereinafter incorporated by reference).
These major improvements, previously detailed by Newman, have concentrated on optimizing the use of energy while reducing overall unit costs while, for the most part, using technology incorporating many of the original system fundamentals. But, by controlling system performance and system efficiency, both the quality and value of the products produced has significantly improved, resulting in an integrated system where cost benefit and product quality potentially outweigh the performance of competing technologies specifically designed for methods of preservation other than sterilization, particularly pasteurization and stabilization.
However, one major obstacle remains, namely, how to optimize and control the physical and chemical properties and performance of the thermal transfer medium when faced with a range of products with different compositions and therefore differing thermal transfer properties.
As previously detailed elsewhere, the use of water as a thermal transfer medium for food and drink product production is extremely inefficient. During any heating phase, it has a thermal transfer rate at least two times faster than needed for producing the best quality food products. As a consequence, a lot of the energy is wasted and too much is consumed by the outer layers of containerized product, resulting in significant over-processing, made worse by any change of state from water to steam. Similar but somewhat less, energy inefficient properties are exhibited during any elevated temperature holding phase, while during cooling phases, water has a relatively small temperature window before it changes state from liquid to solid and becomes extremely abrasive on mechanical systems. Therefore its capability as a cooling agent is physically limiting and process inefficient.
The conundrum for the food manufacturer is an absolute requirement for the production of pathogenically-safe food. However, in doing so, the severe processing conditions cause significant deterioration in food quality attributes. The poorer the food quality attributes, the lower the value of the product. Therefore, there is equally a need for minimal structural disruption in order to maintain the highest product quality.
To achieve sterilization, food has to reach and maintain temperatures of 121° C. for some 5-35 minutes, depending on product type, product composition, container and volume. Higher temperatures and pressures will require less exposure time. Because of very severe limitations on the type and number of chemicals that can directly or indirectly contact food, as well as cost and availability, water has been the primary ‘thermal processing medium of choice’. To achieve sterilization temperatures using water as the thermal transfer medium, requires both a change of state (steam) and a change of pressure (pressurized to 2 atmospheres. Not only does this require a significant amount of energy, in changing from a liquid to its gaseous state, i.e. steam, its thermal conductivity also changes (from 0.58 to 0.016). With most food components (except water and ash) having a thermal conductivity in the range 0.22-0.38 this further exacerbates the issues related to controlled thermal transfer and resultant over-processing, excessive structural breakdown and uneven processing of food and drink products. This makes the use of water as the thermal processing medium costly to structural incorporate and to use and difficult to control in terms of total energy and energy distribution.
It is also extremely corrosive to system structures, especially any equipment or support structures that are constructed of metal and/or concrete with steam being more corrosive than water. It requires considerable extra cost expenditure to minimize these corrosive properties.
While modification, optimization and control of process, product, product container and system performance have all been shown to have positive cost and quality benefits to thermally processed food and drink products, the major cost and performance constraints are the consequence of the thermal capabilities of the processing medium. For a wide range of reasons, there is an obvious and pressing need to find a suitable replacement thermal processing medium for water and steam.
Ideally, this thermal processing medium should be capable of optimized heating, holding and cooling performance without any change of state. Its thermal conductivity also needs to encompass the thermal conductivity of the major components of food and drink products. It also needs to be energy efficient, cost effective, minimally corrosive and safe in use.
While there are many liquids or mixtures that could be used to achieve one or more of these properties, extensive regulatory requirements severely limits which compounds can be used, most particularly in food application uses.
In recent times, there has been considerable advances in the types of thermal transfer media that can be used in cooling applications for buildings, engines, anti-freezes, windscreen washing fluids and the like. Many refrigerant systems use various glycol mixtures or glycol/alcohol mixtures (c.f. U.S. Pat. No. 5,141,662 and USPA 20080048147). These mixtures have found considerable use in such applications because, unlike water they remain in a liquid state when external or operating temperatures fall below 0° C. They have also been suggested as a suitable refrigerant in a wide range of other applications as diverse as solar powered refrigerators (U.S. Pat. No. 7,543,455) and in the cooling of electronic components (USPA 20070122335).
However, all these refrigerant/coolant media still contain significant amounts of water (30%-50% v/v or w/v). As a consequence, they will be ionic in nature and still generate considerable corrosion to metal components, particularly the system's physical structures. As such they need the addition of anti-corrosion compounds to allow them to function as coolants and antifreezes. Eventually, as the temperature falls, some of the water component will form solid ice.
Whereas prior art in the development of thermal processing media has tended to concentrate on cooling applications, more recently there has been a significant increase in the development and application of novel thermal processing heating and holding applications such as solar heating, solar power and geothermal pumps. In such applications, the higher the temperature of the thermal processing media can run, the more efficient and effective the system will perform. As such systems are usually indirect forms of heat exchange, any effective and suitable thermal processing mixture can be used. In such applications, mixtures of glycols have been particularly successful, not only because of their elevated boiling points but also, because of their depressed freezing point capability, to function in climates where there are large temperature differences without any change of state. Once again, such mixtures are ionic and polar in nature and therefore can be extremely corrosive to mechanical parts and constructional components, especially at elevated temperatures.
Whereas most thermal transfer fluids and mixtures have been developed to optimize thermal conductivity, for example, by using carbon nano-capsules to improve the heat dissipation of liquids (USPA 20070122335), it has been suggested (USPA 2006/0051639) that for optimum performance of fuel cells, such equipment needs to maintain elevated temperatures so the thermal transfer fluids used with such systems need to function in a completely different way with high heat capacity but very low thermal conductivity.
Unfortunately, virtually all such compounds and mixtures, as described in the aforesaid application examples, cannot be used in the thermal processing of food applications as they contain components proven to be harmful to humans and animals, even when present in minute quantities.
It is well-known that the number of components approved to directly contact food is both highly regulated and very limited in number. In generally, they tend to be limited to components that are edible in their own right or naturally form part of processed product formulations, such as oils, fats and various water-based mixtures. Alternative fluids also include gas (USPA 2003/0211212) and air. The thermal processing properties of such mixtures usually limit their application to one element of the process. For example, cooking in hot fat and oils is well known. This is usually to ensure the outer surfaces or layers of the treated product are subjected to considerably more heat than the internal layers, e.g. batter coat fish and poultry portions. However, such thermal transfer media cannot be used for product cooling because of poor thermal transfer properties at depressed temperatures such as excessive viscosity or change of state from liquid to solid. Air and gas mixtures are well-known in oven-cooking operations. They are much less energy transfer efficient than liquids in either heating or cooling but they can be temperature better controlled and thus makes them more suitable for food processing applications which require accurate temperature holding for a period of time, e.g. baking of pastries, breads and doughs.
However, most food applications require thermal transfer media with optimized heat transfer properties both during the heating and cooling cycles—one such component is food grade Glycerol (Glycerin)
Glycerin had historically been used as an automobile anti-freeze but was later replaced by more efficient and cheaper glycol mixtures. More recently, with the main source of glycerin/glycerol coming from the manufacture of bio-diesel from renewable resources and from sources other than petroleum, resulting in a much lower supply cost than previously, there has been renewed interest in the use of glycerin/water and glycerin/alcohol/water mixtures as refrigerants (e.g. USPA 20080315152). The use of glycerin as an excellent heating medium has been known for over 2 centuries. It was used to heat absinthe stills in the 19th century so that local overheating from a direct heating source such as a wood or coal fire, would not char the herbs, (Sauron, 2007). It has a high boiling point of 290° C. and a flash point of 176° C. Although generally safe, it does produce Arcolein when decomposed by excessive heat.
Most raw glycerin produced today is a byproduct of biofuel manufacturing, has a typical concentration of 60-82% glycerin but also contains numerous contaminants and other byproducts including glycols, alcohols, particularly methanol and ethanol, various organic and inorganic compounds, fatty acids and water. Unfortunately such compounds, particularly glycols and methanol, are toxic in nature and are not allowed to directly contact foodstuffs, although potentially they could be used as an indirect cooling medium.
In most applications, the use of glycerin/glycerol as a cooling medium is impractical because of increasing viscosity as it cools. Newman (U.S. PA 61/480,521) teaches methods and apparatus that will allow suitable glycerin only or glycerin/minimal water mixtures to function as an effective and efficient coolant, be composed only of GRAS approved components and without the need for anti-corrosion additives, they avoid any constraints in their application or use. Newman further teaches (U.S. PA 61/483,923) how such glycerin based formulations can also be optimally used in conventional hydrostat pasteurization and sterilization technology as well as in novel processing applications in which elevated temperatures are required but as there is no change of state during the heating phase, there is minimal need for pressurization and capital equipment costs are significantly reduced.
However, we have surprisingly found that the thermal transfer properties of such media can be significantly improved if mixed preferentially with other compounds which themselves are GRAS or better approved but have differing transfer properties to glycerol/glycerin mixtures alone in a manner that allows manufacturers to optimize the properties of the thermal transfer medium relative to the thermal transfer properties of the product undergoing processing while maintaining both a single physical state throughout all stages of processing and remain essentially non-corrosive.
We have therefore developed a totally different and novel range of thermal transfer media, which not only addresses all of the constraints, limitations and drawbacks of existing water/steam, based sterilization systems. We have also been able to develop the applications and methodologies to better optimize thermal processing but particularly address energy usage and usage costs.
While these media have been specifically designed for food and drink product manufacture and processing, it will be obvious to those skilled in the art that such controllable thermal transfer media will have application well beyond food and drink manufacturing.